San Francisco Giants thrashed Kansas City Royals 11-4 on Saturday evening in Game Four to level the best-of-seven World Series at 2-2.

The Royals, whose only World Series win came in 1985, managed four runs in the third inning to take a 4-1 lead.

But the hosts, seeking their third title since 2010, levelled in the fifth and then blew away the Royals' bullpen.

Right fielder Hunter Pence led the Giants' rally with three hits and three runs batted in. Game Five is on Sunday.

However, after the teams meet in that game, also at AT&T Park, the series will return to Kansas City's Kauffman Stadium for a sixth - and potentially seventh - match.

Neither starting pitcher made much impression with Giants right-hander Ryan Vogelsong pulled midway through the third inning after the visitors forged ahead, while Royals leftie Jason Vargas did not make it through the fifth, giving up the first three runs as the hosts' rally began.

"These guys fought hard. They scratched and clawed to get back in it," said a delighted Giants manager Bruce Bochy.

"You know you get down against this bullpen, you have your work cut out. But these guys didn't stop fighting."